1. Field of the Invention
This invention relates to oil and gas drilling, and more particularly to apparatus and methods for transmitting data in downhole drilling networks.
2. Background of the Invention
The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have been made to devise a successful system for accessing such drill string data. However, due to the complexity, expense, and unreliability of such systems, many attempts to create such a system have failed to achieve significant commercial acceptance.
In U.S. Pat. No. 6,670,880 issued to Hall et al. (the “Hall patent”), the inventors disclosed a “downhole transmission system” that overcomes many of the problems and limitations of the prior art. In that system, data is transmitted in real time along the drill string by way of network hardware integrated directly into the drill string. This network hardware enables high-speed communication between various tools and sensors, located along the drill string, with surface analysis, diagnostic, and control equipment.
Because the Hall patent solves many of the problems of the prior art by providing a reliable a high-speed connection between downhole drilling components and the surface, novel apparatus and methods are needed to use the connection efficiently. That is, as is currently the case in most transmission systems, bandwidth is limited by the communication hardware involved. Moreover, although the technology described in the Hall patent is a colossal improvement over prior telemetry systems, it is conceivable that the vast array of downhole tools and sensors used in downhole drilling could generate enough data to consume most of the available bandwidth, thereby significantly limiting the number and types of devices that could be connected to the network.
In some cases, bandwidth may be unnecessarily consumed due to inefficient bandwidth allocation. For example, bandwidth may be consumed by needlessly transmitting raw data over the network at times or in quantities that are not needed. In other cases, various downhole components may completely occupy a transmission channel even though data is only transmitted over the channel intermittently. In yet other cases, large amounts of raw data may be transmitted over the network when a much smaller amount of processed data would be sufficient. The foregoing examples, although not an exhaustive list, are illustrative of various ways that the bandwidth of a downhole network may be used inefficiently.
Therefore, in response to various needs felt in the downhole drilling industry, what are needed are apparatus and methods for effectively allocating bandwidth in high-speed downhole telemetry systems. What are further needed are apparatus and methods for effectively sharing bandwidth between downhole devices that transmit data in an inconsistent or intermittent manner. What are further needed are apparatus and methods for efficiently acquiring and receiving signals that are transmitted intermittently or sporadically, in order to conserve bandwidth.